As computer systems become larger and more complex, power management continues to be a major design concern. This is true regardless of whether the computer system is on a large industrial hardware platform or a compact, mobile hardware platform. Power management concerns vary in type and in number between different system platforms. For example, power management is most critical in a mobile system because the system may be required to operate for extended periods on power supplied by a lightweight battery. In mobile systems, power to system components may be shut off under a greater number of conditions than in other systems. In addition, power management schemes differ between hardware platforms depending upon their complexity. A large industrial platform, for example, may use a particular computer system to perform many more tasks involving many more devices than would a mobile platform using a similar computer system.
Prior computer systems have commonly been designed as a set of integrated circuit components that perform different system tasks and are designed to be interconnected. The components of a typical computer system include a processor, a cache memory, a main memory, and one or more bridge devices for handling communications between devices on different buses of the system. For example, in a system with components on an industry standard architecture (ISA) bus and components on a peripheral component interface (PCI) bus, a bridge component is connected to both of the buses and provides a signal path between them.
A typical bridge component between a PCI and an ISA bus includes buffers for temporary storage of data to be transferred, arbitration circuits for gaining control of the PCI bus and the ISA bus and power management circuitry. Power management circuitry typically generates power management signals for transfer to system components from peripheral components. Examples of power management signals are interrupt signals sent to the processor and direct memory access signals sent to the main memory. Power management signals often require the receiving component to exit a low power state.
There are disadvantages associated with the traditional arrangement of computer systems that locates power management circuitry in a system component such as a bridge component. One disadvantage is that such an arrangement requires the component comprising the power management circuitry to include a separate physical path for each inter-component signal indicating a power management event. Different component packages use different arrangements for transmitting signals to and from the component package. An example of a traditional physical signal path is a pin of a dual in-line package (DIP). More recently, components are designed with small solder connections, or balls. Regardless of the component package style or the particular signal paths used, it is desirable to provide a minimum number of inter-component signal paths because they represent space taken in a system and expense in manufacture.
In prior systems, approximately 30 inter-component signal paths are devoted to transmitting signals that indicate power management events.
Another disadvantage is that integrated circuit area is used by the power management circuitry, making the computer system itself larger and more expensive to produce. Another, significant disadvantage exists with prior computer systems that have power management circuitry located on a system component. Power management circuitry is typically designed for the computer system as used with a particular hardware platform, e.g., a desktop platform. If it is desired to use the same system in another platform, e.g., a mobile hardware platform, the power management circuitry is typically not capable of handling the additional power management functions required. When this is the case, it is necessary to adapt the computer system to the hardware platform somehow.
Currently, separate components are used in addition to the computer system components when the computer system components can not handle all power management functions. Usually, these components are microcontrollers that include microcode designed for a particular application. The prior microcontroller components have disadvantages and limitations. A disadvantage is that the microcontroller requires a separate inter-component signal path for each signal it may receive indicating a power management event. This makes the microcontroller component large. A limitation of prior microcontroller power management components is that they are coupled to the ISA bus rather than to the PCI bus. For this reason, prior power management components cannot monitor the PCI bus, detect central processing unit (CPU) and PCI bus activity relating to power management and respond by transmitting appropriate signals.
What is needed is a computer system that is portable between hardware platforms and that does not require extensive circuitry and inter-component signal paths for power management. A separate power management component is also needed to operate with the computer system on different hardware platforms and efficiently handle all power management events associated with the hardware platform.
The present invention provides a method and apparatus for allowing a particular computer system to operate on different hardware platforms without the addition of extra circuitry or inter-component signal paths to handle power management events that are unique to a particular hardware platform.